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Understanding Video Bitrate: Essential for High-Quality Video Encoding | Datavideo

Understanding Video Bitrate: Essential for High-Quality Video Encoding

Mar 28 2022

Once you are finished editing your video, the next phase in video production is to encode your video. Video encoding plays a critical role in ensuring streaming quality. In network streaming, H.264 is the most widely used codec, with the generated video packaged into MP4 format. A critical factor determining image quality is the “bitrate” which we would like to talk about in this article.

What is a bitrate?

A bitrate is also known as bit rate or compression rate. A video bitrate is the number of bits that are processed in a unit of time. An encoder applies a higher bitrate per unit time; the lower compression ratio used for the video improves image quality. On the contrary, more compressed files have lower bitrates, resulting in an awful viewing experience. Thus, the bitrate is proportional to the image quality, but the video file’s size also increases as the bitrate increases.

We can calculate the video file’s size by the given bitrate. For example, if three-minute footage is recorded at 6000 kbits per second (or 750KBytes per second), the bitrate in KBytes per second (750KBytes per second) is multiplied by the footage duration (180 seconds) to yield 135,000KB which equals 131.8 MB (135000KB/ 1024).

Note: Video bitrate is often measured in kilobits per second (kbps) or Megabits per second (MBps). A byte is an uppercase B, and a bit is a lowercase b. One byte consists of 8 bits.

Video encoding attempts to balance compression rate and image quality to create a smaller file size and higher-quality video. Applying high bitrates is not always the best choice because it is difficult for the human eye to detect the slight difference when the extremely high resolution is beyond visual perception.

Since the lower video bitrate requires less network bandwidth, thus a user can lower the video bitrate to ensure the stable and no buffering video playing where the network service is poor.

Constant Bitrate (CBR) and Variable Bitrate (VBR)

The Common bitrate settings include CBR (Constant Bitrate) and VBR (Variable Bitrate). The variable bitrate means that the encoder provides more bitrate to compress the more complex segments of frames while less space is allocated to less complicated details. The VBR is suitable for most productions, especially if there are a lot of randomly moving objects in the video, such as raindrops or heavy snow. The CBR applies the constant bitrate to compress the video by the given file size. CBR is appropriate for video production with little or no variability in the background, such as the conference and interview videos. CBR ensures a constant flow of data so that the video will not freeze or buzz while streaming video to the platform.

Bitrate and Network Speed

Most live-streaming platforms, such as YouTube, Vimeo, Facebook, etc., compress the uploaded video. The platform initially compresses video at a low bitrate so that the video is available to stream on a wide variety of devices.

Take uploading a 1080p video on the YouTube platform as an example. YouTube compresses the video bitrate to 6000Kbs. The video can be played smoothly as long as the network speed exceeds 6Mb. On the contrary, if the video is not compressed, assuming that the original bitrate is 20Mb, the network speed must be above 20Mb to support smoothly playing video.

Recommended bitrate settings provided by YouTube are shown in the below table. Please note that these settings may vary on other platforms.